Well it depends on what you are breeding, if you are crossing Amphilophus with another Amphilophus its gonna be fertile but if your crossing Amphilophus with say Herichthys then you are crossing outside the genus and can get sterility.
And (hopefully soon) I wont have to deal with any of those problems. Every cross I make after the first one will be back to the orginal pure species. Even though 75% pure should be enough to produce fertile males I still intend to continue to introduce pure blood.